Context

The role that represents an application of a term macro, e.g. M(2)(3) in val x = M(2)(3) or M(a, b) in x match { case x @ M(a, b) => }.

A shorthand to create an expr.

Unlike the conventional expr factory, which requires a scala.reflect.api.TreeCreator, this one accepts a regular tree, but the resulting exprs are unable of being migrated to other universes/mirrors (the functionality normally not needed for macros, since there is only one compile-time universe and only one compile-time mirror).

A shorthand to create a type tag.

Unlike the conventional type tag factory, which requires a scala.reflect.api.TypeCreator, this one accepts a regular type, but the resulting type tags are unable of being migrated to other universes/mirrors (the functionality normally not needed for macros, since there is only one compile-time universe and only one compile-time mirror).

A shorthand to create a weak type tag.

Unlike the conventional type tag factory, which requires a scala.reflect.api.TypeCreator, this one accepts a regular type, but the resulting type tags are unable of being migrated to other universes/mirrors (the functionality normally not needed for macros, since there is only one compile-time universe and only one compile-time mirror).

Abruptly terminates current macro expansion leaving a note about what happened. Use enclosingPosition if you're in doubt what position to pass to pos.

Exposes current classpath.

Exposes current compiler settings as a list of options. Use scalac -help, scalac -X and scalac -Y to learn about currently supported options.

For sending a message which should not be labeled as a warning/error, but also shouldn't require -verbose to be visible. Use enclosingPosition if you're in doubt what position to pass to pos.

Tree that corresponds to the enclosing DefDef tree. Throws EnclosureException if there's no such enclosing tree.

Tree that corresponds to the enclosing ImplDef tree (i.e. either ClassDef or ModuleDef). Throws EnclosureException if there's no such enclosing tree.

Types along with corresponding trees for which implicit arguments are currently searched. Can be useful to get information about an application with an implicit parameter that is materialized during current macro expansion.

Unlike openImplicits, this is a val, which means that it gets initialized when the context is created and always stays the same regardless of whatever happens during macro expansion.

Contexts that represent macros in-flight, including the current one. Very much like a stack trace, but for macros only. Can be useful for interoperating with other macros and for imposing compiler-friendly limits on macro expansion.

Is also priceless for emitting sane error messages for macros that are called by other macros on synthetic (i.e. position-less) trees. In that dire case navigate the enclosingMacros stack, and it will most likely contain at least one macro with a position-ful macro application. See enclosingPosition for a default implementation of this logic.

Unlike openMacros, this is a val, which means that it gets initialized when the context is created and always stays the same regardless of whatever happens during macro expansion.

Tree that corresponds to the enclosing PackageDef tree. Throws EnclosureException if there's no such enclosing tree.

Tries to guess a position for the enclosing application. But that is simple, right? Just dereference pos of macroApplication? Not really. If we're in a synthetic macro expansion (no positions), we must do our best to infer the position of something that triggerd this expansion. Surprisingly, quite often we can do this by navigation the enclosingMacros stack.

Compilation run that contains this macro application.

Tree that corresponds to the enclosing Template tree. Throws EnclosureException if there's no such enclosing tree.

Compilation unit that contains this macro application.

Emits a compilation error. Use enclosingPosition if you're in doubt what position to pass to pos.

Takes a typed wrapper for a tree of type T and evaluates it to a value of type T.

Can be used to perform compile-time computations on macro arguments to the extent permitted by the shape of the arguments.

Known issues: because of https://issues.scala-lang.org/browse/SI-5748 trees being evaluated first need to undergo resetAllAttrs. Resetting symbols and types mutates the tree in place, therefore the conventional approach is to duplicate the tree first.

scala> def impl(c: Context)(x: c.Expr[String]) = {
     | val x1 = c.Expr[String](c.resetAllAttrs(x.tree.duplicate))
     | println(s"compile-time value is: ${c.eval(x1)}")
     | x
     | }
impl: (c: Context)(x: c.Expr[String])c.Expr[String]

scala> def test(x: String) = macro impl
test: (x: String)String

scala> test("x")
compile-time value is: x
res0: String = x

scala> test("x" + "y")
compile-time value is: xy
res1: String = xy

scala> val x = "x"
x: String = x

scala> test(x + "y")
compile-time value is: xy
res2: String = xy

scala> { val x = "x"; test(x + "y") }
error: exception during macro expansion:
scala.tools.reflect.ToolBoxError: reflective compilation failed

Note that in the last case evaluation has failed, because the argument of a macro refers to a runtime value x, which is unknown at compile time.

Creates a unique name having a given name as a prefix and having the same flavor (term name or type name) as the given name.

Creates a unique string having a given prefix.

Creates a unique string.

Does the compilation session have any errors?

Does the compilation session have any warnings?

Infers an implicit value of the expected type pt in the macro callsite context. Optional pos parameter provides a position that will be associated with the implicit search.

If silent is false, TypecheckException will be thrown in case of an inference error. If silent is true, the typecheck is silent and will return EmptyTree if an error occurs. Such errors don't vanish and can be inspected by turning on -Xlog-implicits. Unlike in typeCheck, silent is true by default.

Infers an implicit view from the provided tree tree of the type from to the type to in the macro callsite context. Optional pos parameter provides a position that will be associated with the implicit search.

If silent is false, TypecheckException will be thrown in case of an inference error. If silent is true, the typecheck is silent and will return EmptyTree if an error occurs. Such errors don't vanish and can be inspected by turning on -Xlog-implicits. Unlike in typeCheck, silent is true by default.

Emits an informational message, suppressed unless -verbose or force=true. Use enclosingPosition if you're in doubt what position to pass to pos.

Adds a list of top-level definitions to the compiler's symbol table. _TOP_LEVEL Allowed definitions include classes (represented by ClassDef trees), traits (represented by ClassDef trees having the TRAIT flag set in mods) and objects (represented by ModuleDef trees).

The definitions are put into the package with a prototype provided in packagePrototype. Supported prototypes are (see PackageSpec for more details): * Strings and names representing a fully-qualified name of the package * Trees that can work as package ids * Package or package class symbols

Typical value for a package prototype is a fully-qualified name in a string. For example, to generate a class available at foo.bar.Test, call this method as follows:

introduceTopLevel("foo.bar", ClassDef(<mods>, TypeName("Test"), <tparams>, <template>))

It is possible to add definitions to the empty package by using nme.EMPTY_PACKAGE_NAME.toString, but that's not recommended, since such definitions cannot be seen from outside the empty package.

Only the multi-parameter overload of this method can be used to introduce companions. If companions are introduced by two different calls, then they will be put into different virtual files, and scalac will show an error about companions being defined in different files. By the way, this also means that there's currently no way to define a companion for an existing class or module_TOP_LEVEL.

Returns a list of fully-qualified references to the introduced definitions.

Adds a top-level definition to the compiler's symbol table. _TOP_LEVEL Allowed definitions include classes (represented by ClassDef trees), traits (represented by ClassDef trees having the TRAIT flag set in mods) and objects (represented by ModuleDef trees).

The definitions are put into the package with a prototype provided in packagePrototype. Supported prototypes are (see PackageSpec for more details): * Strings and names representing a fully-qualified name of the package * Trees that can work as package ids * Package or package class symbols

Typical value for a package prototype is a fully-qualified name in a string. For example, to generate a class available at foo.bar.Test, call this method as follows:

introduceTopLevel("foo.bar", ClassDef(<mods>, TypeName("Test"), <tparams>, <template>))

It is possible to add definitions to the empty package by using nme.EMPTY_PACKAGE_NAME.toString, but that's not recommended, since such definitions cannot be seen from outside the empty package.

Only the multi-parameter overload of this method can be used to introduce companions. If companions are introduced by two different calls, then they will be put into different virtual files, and scalac will show an error about companions being defined in different files. By the way, this also means that there's currently no way to define a companion for an existing class or module_TOP_LEVEL.

Returns a fully-qualified reference to the introduced definition.

Shorthand for Literal(Constant(x: Char)) in the underlying universe.

Shorthand for Literal(Constant(x: String)) in the underlying universe.

Shorthand for Literal(Constant(x: Double)) in the underlying universe.

Shorthand for Literal(Constant(x: Float)) in the underlying universe.

Shorthand for Literal(Constant(x: Long)) in the underlying universe.

Shorthand for Literal(Constant(x: Int)) in the underlying universe.

Shorthand for Literal(Constant(x: Short)) in the underlying universe.

Shorthand for Literal(Constant(x: Byte)) in the underlying universe.

Shorthand for Literal(Constant(x: Boolean)) in the underlying universe.

Shorthand for Literal(Constant(false)) in the underlying universe.

Shorthand for Literal(Constant(null)) in the underlying universe.

Shorthand for Literal(Constant(true)) in the underlying universe.

Shorthand for Literal(Constant(())) in the underlying universe.

The tree that undergoes macro expansion. Can be useful to get an offset or a range position of the entire tree being processed.

The semantic role that macroApplication plays in the code.

Types along with corresponding trees for which implicit arguments are currently searched. Can be useful to get information about an application with an implicit parameter that is materialized during current macro expansion.

Unlike enclosingImplicits, this is a def, which means that it gets recalculated on every invocation, so it might change depending on what is going on during macro expansion.

Contexts that represent macros in-flight, including the current one. Very much like a stack trace, but for macros only. Can be useful for interoperating with other macros and for imposing compiler-friendly limits on macro expansion.

Is also priceless for emitting sane error messages for macros that are called by other macros on synthetic (i.e. position-less) trees. In that dire case navigate the openMacros stack, and it will most likely contain at least one macro with a position-ful macro application. See enclosingPosition for a default implementation of this logic.

Unlike enclosingMacros, this is a def, which means that it gets recalculated on every invocation, so it might change depending on what is going on during macro expansion.

Parses a string with a Scala expression into an abstract syntax tree. Only works for expressions, i.e. parsing a package declaration will fail.

The prefix tree from which the macro is selected.

For example, for a macro filter defined as an instance method on a collection Coll, prefix represents an equivalent of this for normal instance methods:

scala> class Coll[T] {
     | def filter(p: T => Boolean): Coll[T] = macro M.filter[T]
     | }; object M {
     | def filter[T](c: Context { type PrefixType = Coll[T] })
     |              (p: c.Expr[T => Boolean]): c.Expr[Coll[T]] =
     |   {
     |     println(c.prefix.tree)
     |     c.prefix
     |   }
     | }
defined class Coll
defined module Macros

scala> new Coll[Int]().filter(_ % 2 == 0)
new Coll[Int]()
res0: Coll[Int] = ...

scala> val x = new Coll[String]()
x: Coll[String] = ...

scala> x.filter(_ != "")
$line11.$read.$iw.$iw.$iw.$iw.$iw.$iw.$iw.$iw.$iw.$iw.$iw.$iw.x
res1 @ 35563b4b: x.type = ...

Note how the value of prefix changes depending on the qualifier of the macro call (i.e. the expression that is at the left-hand side of the dot).

Another noteworthy thing about the snippet above is the Context { type PrefixType = Coll[T] } type that is used to stress that the macro implementation works with prefixes of type Coll[T].

Given a type, generate a tree that when compiled and executed produces the runtime class of the enclosing class or module. Returns EmptyTree if there does not exist an enclosing class or module.

Given a type, generate a tree that when compiled and executed produces the runtime class of the original type. If concrete is true, then this function will bail on types, who refer to abstract types (like ClassTag does).

Given a tree, generate a tree that when compiled and executed produces the original tree. For more information and examples see the documentation for Universe.reify.

The produced tree will be bound to the specified universe and mirror. Possible values for universe include universe.treeBuild.mkRuntimeUniverseRef. Possible values for mirror include EmptyTree (in that case the reifier will automatically pick an appropriate mirror).

This function is deeply connected to Universe.reify, a macro that reifies arbitrary expressions into runtime trees. They do very similar things (Universe.reify calls Context.reifyTree to implement itself), but they operate on different metalevels (see below).

Let's study the differences between Context.reifyTree and Universe.reify on an example of using them inside a fooMacro macro:

* Since reify itself is a macro, it will be executed when fooMacro is being compiled (metalevel -1) and will produce a tree that when evaluated during macro expansion of fooMacro (metalevel 0) will recreate the input tree.

This provides a facility analogous to quasi-quoting. Writing "reify{ expr }" will generate an AST that represents expr. Afterwards this AST (or its parts) can be used to construct the return value of fooMacro.

* reifyTree is evaluated during macro expansion (metalevel 0) and will produce a tree that when evaluated during the runtime of the program (metalevel 1) will recreate the input tree.

This provides a way to retain certain trees from macro expansion time to be inspected later, in the runtime. For example, DSL authors may find it useful to capture DSL snippets into ASTs that are then processed at runtime in a domain-specific way.

Also note the difference between universes of the runtime trees produced by two reifies:

* The result of compiling and running the result of reify will be bound to the Universe that called reify. This is possible because it's a macro, so it can generate whatever code it wishes.

* The result of compiling and running the result of reifyTree will be the prefix that needs to be passed explicitly. This happens because the Universe of the evaluated result is from a different metalevel than the Context the called reify.

Typical usage of this function is to retain some of the trees received/created by a macro into the form that can be inspected (via pattern matching) or compiled/run (by a reflective ToolBox) during the runtime.

Given a type, generate a tree that when compiled and executed produces the original type. The produced tree will be bound to the specified universe and mirror. For more information and examples see the documentation for Context.reifyTree and Universe.reify.

Recursively resets symbols and types in a given tree.

Note that this does not revert the tree to its pre-typer shape. For more info, read up https://issues.scala-lang.org/browse/SI-5464.

Recursively resets locally defined symbols and types in a given tree.

Note that this does not revert the tree to its pre-typer shape. For more info, read up https://issues.scala-lang.org/browse/SI-5464.

Exposes macro-specific settings as a list of strings. These settings are passed to the compiler via the "-Xmacro-settings:setting1,setting2...,settingN" command-line option.

Looks up a top-level definition tree with a given fully-qualified name (term name for modules, type name for classes). _TREE Top-level tree is a tree that represents a non-inner class or object in one of the currently compiled source files. Note that top-level isn't equivalent to scala.reflect.api.Symbols#SymbolApi.isStatic, because static also embraces definitions nested in static objects _TREE. If such a tree does not exist, returns EmptyTree.

Returns a reference to a top-level definition tree with a given fully-qualified name (term name for modules, type name for classes). _TREE Top-level tree is a tree that represents a non-inner class or object in one of the currently compiled source files. Note that top-level isn't equivalent to scala.reflect.api.Symbols#SymbolApi.isStatic, because static also embraces definitions nested in static objects _TREE. If such a tree does not exist, returns EmptyTree.

Typechecks the provided tree against the expected type pt in the macro callsite context.

If silent is false, TypecheckException will be thrown in case of a typecheck error. If silent is true, the typecheck is silent and will return EmptyTree if an error occurs. Such errors don't vanish and can be inspected by turning on -Ymacro-debug-verbose. Unlike in inferImplicitValue and inferImplicitView, silent is false by default.

Typechecking can be steered with the following optional parameters: withImplicitViewsDisabled recursively prohibits implicit views (though, implicit vals will still be looked up and filled in), default value is false withMacrosDisabled recursively prohibits macro expansions and macro-based implicits, default value is false

Undoes reification of a tree.

This reversion doesn't simply restore the original tree (that would lose the context of reification), but does something more involved that conforms to the following laws:

1) unreifyTree(reifyTree(tree)) != tree // unreified tree is tree + saved context // in current implementation, the result of unreify is opaque // i.e. there's no possibility to inspect underlying tree/context

2) reifyTree(unreifyTree(reifyTree(tree))) == reifyTree(tree) // the result of reifying a tree in its original context equals to // the result of reifying a tree along with its saved context

3) compileAndEval(unreifyTree(reifyTree(tree))) ~ compileAndEval(tree) // at runtime original and unreified trees are behaviorally equivalent

Emits a warning. Use enclosingPosition if you're in doubt what position to pass to pos.

Tree that corresponds to the enclosing class, or EmptyTree if not applicable.

Tree that corresponds to the enclosing method, or EmptyTree if not applicable.

Creates a unique name having a given name as a prefix and having the same flavor (term name or type name) as the given name.

Creates a unique string having a given prefix.

Creates a unique string.

Constructor/Extractor for Expr.

Constructor/Extractor for TypeTag.

Constructor/Extractor for WeakTypeTag.

Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).

Shortcut for implicitly[TypeTag[T]].tpe

Shortcut for implicitly[TypeTag[T]]

Shortcut for implicitly[WeakTypeTag[T]].tpe

Shortcut for implicitly[WeakTypeTag[T]]